Field of the Invention
The present invention relates in a general manner to a method for printing a pattern, referred to as marking, which is preferably temporary, via inkjet printing on a surface, in particular a hydrophobic surface and more particularly the surface of an optical article and more specifically of an ophthalmic lens such as a spectacle lens.
The present invention also relates to an optical article, especially a lens and more particularly an ophthalmic lens such as a spectacle lens, on a main surface of which a preferably temporary ink marking is formed.
Description of the Related Art
It is known to print a marking on a surface of a substrate, especially of an optical article and more particularly of an ophthalmic lens, by means of an ink jet.
In the case of ophthalmic lenses such as spectacle lenses, the objective of this printing, of an ink marking on a surface of the lens also referred to as marking out, is to enable the alignment and the control of the alignment of finished ophthalmic lenses, that is to say ophthalmic lenses that have been polished and that have received the added values (scratch-resistant, impact-resistant, anti-reflective, anti-soiling, etc. coatings), for the subsequent treatment steps of the finished ophthalmic lenses, in particular the cutting of the finished ophthalmic lenses in order to shape them to the size and shape of a frame or the piercing of these ophthalmic lenses in order to attach them to a frame.
These finished ophthalmic lenses are generally stored in envelopes, for example paper envelopes, before the final treatments, in particular edging. During the transport of these finished lenses in their envelope, the material of the envelope rubs on the main surfaces of the finished lenses, which results in total or partial destruction of the printed markings. This possibly having the effect of increasing the difficulties of control and of alignment of the finished ophthalmic lenses for the subsequent treatment steps such as cutting or even of rendering these steps impossible, and furthermore possibly having a negative effect on the customer regarding the perception of the quality of the product and service provided.
It is important to note that marking out may also be carried out on semi-finished lenses, that have not been polished on the rear face, with or without added values on the front face, or even on cut ophthalmic lenses, that is to say finished ophthalmic lenses that have been cut in the shape of the frame. The invention is not therefore limited to marking out on finished ophthalmic lenses.
In the case of non-wetting surfaces, for example for hydrophobic surfaces, the drops of ink deposited and solidified generally have a weak adhesion to the surface, which results in a faster destruction of the printed markings during the transport of the lenses.
Moreover, in the case of hydrophobic surfaces, the ease of coalescence of the ink drops degrades the quality of the outline. This coalescence phenomenon has been shown schematically in FIG. 1 and consists of a joining of several ink drops initially deposited side-by-side, due to the surface tension of the ink drops and their mobility on the substrate, in order to form ink spots that are generally separate, of larger dimension and of imprecise shapes. This results in a deformation and a loss of sharpness of the marking. Generally, in order to prevent the problems of coalescence, it may be necessary to deposit the drops with a lower kinetic energy, which generally results in markings that are not as clearly defined.
Thus, the printings of inkjet markings from the prior art on a main surface of a finished ophthalmic lens, especially on a hydrophobic surface, encounter two major difficulties:
a poor definition of the outline of the marking due to the coalescence of the ink drops; and
a poor mechanical hold which results in complete or partial deletion of the marking when the finished ophthalmic lens is handled in its packaging.
In order to increase the adhesion of the ink marking to the surface of a substrate, especially hydrophobic surface, it has been proposed to modify the surface adhesion: either by covering the substrate with a temporary tie layer made of an adherent material that aims to increase the adhesion of the ink to the substrate, or by developing specific inks that adhere better to the surfaces, especially hydrophobic surfaces, of the substrates, that is to say that have a lower static contact angle.
The first solution, consisting in depositing a temporary tie layer, necessitates introducing an additional step into the manufacture of the optical article, thus increasing the cost, and necessitating its, generally manual, removal at the end of the operations.
The second solution, use of specific inks, requires significant development fees and substantially increases the manufacturing costs of the optical articles.
These solutions from the prior art are described, inter alia, in application EP 1 392 613.
Other solutions, for example described in application EP 2 487 039, propose selecting an ink that can be polymerized by means of ultraviolet rays and also a drop size and a drop density that prevent any drop superposition and polymerizing each drop, one after the other, immediately after the deposition thereof in order to avoid coalescence of the drops.